Tire with component containing polybenzobisoxazole short fiber and epoxidized palm oil

ABSTRACT

The present invention is directed to a pneumatic tire comprising at least one component, the at least one component comprising a rubber composition, the rubber composition comprising a diene based elastomer and from 1 to 30 parts by weight, per 100 parts by weight of elastomer, of a polybenzobisoxazole (PBO) short fiber having a length ranging from 0.5 to 20 mm and a thickness ranging from 10 to 30 microns, and from 1 to 30 parts by weight, per 100 parts by weight of elastomer, of an epoxidized palm oil.

BACKGROUND OF THE INVENTION

A tire is a composite of several components each serving a specific andunique function yet all synergistically functioning to produce thedesired performance. One important component is the carcass ply. Thecarcass ply is a continuous layer of rubber-coated parallel cords whichextends from bead to bead and functions as a reinforcing element of thetire. The ply is turned-up around the bead, thereby locking the beadinto the assembly or carcass. In the immediate proximity of the carcassply turn-up is an apex. The apex includes a rubber wedge located in thelower sidewall region above the bead and is bonded to and encased by thecarcass plies. The apex also includes the area located between the lowersidewall rubber and the axially outer side of the carcass ply turn-up.Between the bead and apex, a flipper may be included, and between thecarcass ply and chafer, a chipper may be included. The apex serves tostiffen the area near the bead in the lower sidewall. The flipper servesas an interface between the bead and carcass ply, to prevent erosion ofthe carcass ply and/or bead due to interfacial stresses. The chipperserves as an interface between the carcass ply and the rubber chafercontacting the wheel rim.

The apex, flipper and chipper performance may improve when reinforcedwith short fibers having a specific orientation. For example, an apexwith radially oriented fibers may improve the bending stiffness of thelower sidewall of the tire. Known techniques for orienting reinforcingshort fibers in an elastomeric material are generally methods fororienting fibers in a composite in a direction which is consistent withand parallel to the material flow direction in processing equipment.However, such fiber orientation is often difficult to achieve inpractice due to poor dispersion and/or adhesion of the fibers to therubber. There is, therefore, a need for an improved apex, flipper, orchipper with oriented short fibers.

SUMMARY OF THE INVENTION

The present invention is directed to a pneumatic tire comprising atleast one component, the at least one component comprising a rubbercomposition, the rubber composition comprising a diene based elastomerand from 1 to 30 parts by weight, per 100 parts by weight of elastomer,of a polybenzobisoxazole (PBO) short fiber having a length ranging from0.5 to 20 mm having a thickness ranging from 10 to 30 microns and from 1to 30 parts by weight, per 100 parts by weight of elastomer, of anepoxidized palm oil.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a cross-section of a portion of a tire according to oneembodiment of the present invention.

FIG. 2 is a graph of stress vs strain measured for several samples.

FIG. 3 is a graph of stress ratio vs strain measured for severalsamples.

DETAILED DESCRIPTION OF THE INVENTION

There is disclosed a pneumatic tire comprising at least one component,the at least one component comprising a rubber composition, the rubbercomposition comprising a diene based elastomer, from 1 to 30 parts byweight, per 100 parts by weight of elastomer, of a polybenzobisoxazoleshort fiber having a length ranging from 0.5 to 20 mm, having athickness ranging from 10 to 30 microns, and from 1 to 30 parts byweight, per 100 parts by weight of elastomer, of an epoxidized palm oil.

The rubber composition includes a polybenzobisoxazole short fiber. Inone embodiment, suitable polybenzobisoxazole fiber is produced bymethods as taught for example in U.S. Pat. No. 5,976,447, the teachingsof both of which are fully incorporated herein by reference. Afterproduction of polymeric fiber, the fiber may be cut to the desiredlength by methods as are known in the art.

Suitable polybenzobisoxazole fibers can be produced as disclosed in U.S.Pat. No. 5,976,447. As taught therein, fibers prepared frompolybenzobisoxazole (PBO) may be prepared by first extruding a solutionof polybenzobisoxazole polymer in a mineral acid (a polymer “dope”)through a die or spinneret to prepare a dope filament. The dope filamentis then drawn across an air gap, washed in a bath comprising water or amixture of water and a mineral acid, and then dried. If multiplefilaments are extruded simultaneously, they may then be combined into amultifilament fiber before, during, or after the washing step. The woundlong fiber may then be cut to the desired short lengths using methods asare known in the art.

In one embodiment, the PBO fiber may be treated with an adhesivecomposition to improve the adhesion of the PBO short fiber to rubber.For example and in one embodiment, prior to cutting the long PBO fiberto the desired short lengths, the long fiber may be dipped in aconventional RFL type treatment. In one embodiment and as taught in U.S.Pat. No. 6,824,871, wherein PBO yarn or cord is coated with a mixture ofan epoxy resin with a vinyl pyridine-styrene-butadiene rubber latex(VPSBRL), the mixture referred to as a “subcoat”; the subcoated cord isthen again coated by dipping in a conventional reaction product of aphenolic compound, an aldehyde donor and a latex, familiarly referred togenerically as a “resorcinol-formaldehyde latex (RFL)”; and, (B) to aPBO-finishing process to make twice-coated yarn, in which process theepoxy-latex mixture is applied to PBO yarn which may have been given aspin-finish, or corona, or plasma treatment, yielding subcoated PBOyarn; and, the subcoated yarn is then again coated by dipping in aconventional RFL dip.

In one embodiment, the polybenzobisoxazole short fiber has an averagelength of from 0.5 to 20 mm. In one embodiment, the polybenzobisoxazoleshort fiber has an average length of from 1 to 10 mm. In one embodiment,the polybenzobisoxazole short fiber has an average thickness of from 10to 30 microns. In one embodiment, the polybenzobisoxazole short fiberhas an average thickness of from 10 to 20 microns. In one embodiment,the polybenzobisoxazole short fiber has a weight ranging from 0.5 to 5decitex.

Suitable PBO fiber is available commercially as Zylon® from Toyobo.

In one embodiment, the polybenzobisoxazole short fiber is present in therubber composition in a concentration ranging from 1 to 100 parts byweight per 100 parts by weight of diene based elastomer (phr). Inanother embodiment, the polybenzobisoxazole short fiber is present inthe rubber composition in a concentration ranging from 5 to 50 parts byweight per 100 parts by weight of diene based elastomer (phr). Inanother embodiment, the polybenzobisoxazole short fiber is present inthe rubber composition in a concentration ranging from 10 to 30 parts byweight per 100 parts by weight of diene based elastomer (phr).

The rubber composition also includes an epoxidized palm oil. Suitableepoxidized palm oil may be produced using methods as described in WO2007/123637, fully incorporated herein by reference. As taught therein,palm oil refers to the oil derived from the mesocarp of the oil palmfruit. Palm oils typically a semi-solid at room temperature andcomprises about 50% saturated fatty acids and about 50% unsaturatedfatty acids. Palm oil typically comprises predominantly fatty acidtriglycerides, although monoglycerides and diglycerides may also bepresent in small amounts. The fatty acids typically have chain lengthsranging from about C12 to about C20. Representative saturated fattyacids include, for example, C12:0, C14:0, C16:0, C18:0, and C20:0saturated fatty acids. Representative unsaturated fatty acids include,for example, C16:1, C18:1, C18:2, and C18:3 unsaturated fatty acids.

A partially- or fully-epoxidized palm oil composition may be prepared byreacting a palm oil with a peroxyacid under conditions that convert aportion of or substantially all of the double bonds that are present inthe palm-based oil to epoxide groups. Partially-epoxidized palm oils mayinclude at least about 10%, at least about 20%, at least about 25%, atleast about 30%, at least about 35%, at least about 40% or more of theoriginal amount of double bonds present in the palm oil. The partiallyepoxidized palm oil may include up to about 90%, up to about 80%, up toabout 75%, up to about 70%, up to about 65%, up to about 60%, or fewerof the original amount of double bonds present in the palm oil.Fully-epoxidized palm oil may include up to about 10%, up to about 5%,up to about 2%, up to about 1%, or fewer of the original amount ofdouble bonds present in the palm oil.

In one embodiment, the epoxidized palm oil contains from 1 to 5 percentof unsaturated bonds converted to epoxy groups. In one embodiment, theepoxidized polyisoprene contains from 2 to 4 percent of unsaturatedbonds converted to epoxy groups.

Suitable epoxidized palm oil is available commercially, for example asUltraflex EPO from Performance Additives.

The rubber composition may be used with rubbers or elastomers containingolefinic unsaturation. The phrases “rubber or elastomer containingolefinic unsaturation” or “diene based elastomer” are intended toinclude both natural rubber and its various raw and reclaim forms aswell as various synthetic rubbers. In the description of this invention,the terms “rubber” and “elastomer” may be used interchangeably, unlessotherwise prescribed. The terms “rubber composition,” “compoundedrubber” and “rubber compound” are used interchangeably to refer torubber which has been blended or mixed with various ingredients andmaterials and such terms are well known to those having skill in therubber mixing or rubber compounding art. Representative syntheticpolymers are the homopolymerization products of butadiene and itshomologues and derivatives, for example, methylbutadiene,dimethylbutadiene and pentadiene as well as copolymers such as thoseformed from butadiene or its homologues or derivatives with otherunsaturated monomers. Among the latter are acetylenes, for example,vinyl acetylene; olefins, for example, isobutylene, which copolymerizeswith isoprene to form butyl rubber; vinyl compounds, for example,acrylic acid, acrylonitrile (which polymerize with butadiene to formNBR), methacrylic acid and styrene, the latter compound polymerizingwith butadiene to form SBR, as well as vinyl esters and variousunsaturated aldehydes, ketones and ethers, e.g., acrolein, methylisopropenyl ketone and vinylethyl ether. Specific examples of syntheticrubbers include neoprene (polychloroprene), polybutadiene (includingcis-1,4-polybutadiene), polyisoprene (including cis-1,4-polyisoprene),butyl rubber, halobutyl rubber such as chlorobutyl rubber or bromobutylrubber, styrene/isoprene/butadiene rubber, copolymers of 1,3-butadieneor isoprene with monomers such as styrene, acrylonitrile and methylmethacrylate, as well as ethylene/propylene terpolymers, also known asethylene/propylene/diene monomer (EPDM), and in particular,ethylene/propylene/dicyclopentadiene terpolymers. Additional examples ofrubbers which may be used include alkoxy-silyl end functionalizedsolution polymerized polymers (SBR, PBR, IBR and SIBR), silicon-coupledand tin-coupled star-branched polymers. The preferred rubber orelastomers are polyisoprene (natural or synthetic), polybutadiene andSBR.

In one aspect the rubber is preferably of at least two of diene basedrubbers. For example, a combination of two or more rubbers is preferredsuch as cis 1,4-polyisoprene rubber (natural or synthetic, althoughnatural is preferred), 3,4-polyisoprene rubber,styrene/isoprene/butadiene rubber, emulsion and solution polymerizationderived styrene/butadiene rubbers, cis 1,4-polybutadiene rubbers andemulsion polymerization prepared butadiene/acrylonitrile copolymers.

In one aspect of this invention, an emulsion polymerization derivedstyrenelbutadiene (E-SBR) might be used having a relatively conventionalstyrene content of about 20 to about 28 percent bound styrene or, forsome applications, an E-SBR having a medium to relatively high boundstyrene content, namely, a bound styrene content of about 30 to about 45percent.

By emulsion polymerization prepared E-SBR, it is meant that styrene and1,3-butadiene are copolymerized as an aqueous emulsion. Such are wellknown to those skilled in such art. The bound styrene content can vary,for example, from about 5 to about 50 percent. In one aspect, the E-SBRmay also contain acrylonitrile to form a terpolymer rubber, as E-SBAR,in amounts, for example, of about 2 to about 30 weight percent boundacrylonitrile in the terpolymer.

Emulsion polymerization prepared styrenelbutadiene/acrylonitrilecopolymer rubbers containing about 2 to about 40 weight percent boundacrylonitrile in the copolymer are also contemplated as diene basedrubbers for use in this invention.

The solution polymerization prepared SBR (S-SBR) typically has a boundstyrene content in a range of about 5 to about 50, preferably about 9 toabout 36, percent. The S-SBR can be conveniently prepared, for example,by organo lithium catalyzation in the presence of an organic hydrocarbonsolvent.

In one embodiment, cis 1,4-polybutadiene rubber (BR) may be used. SuchBR can be prepared, for example, by organic solution polymerization of1,3-butadiene. The BR may be conveniently characterized, for example, byhaving at least a 90 percent cis 1,4-content.

The cis 1,4-polyisoprene and cis 1,4-polyisoprene natural rubber arewell known to those having skill in the rubber art.

The term “phr” as used herein, and according to conventional practice,refers to “parts by weight of a respective material per 100 parts byweight of rubber, or elastomer.”

The rubber composition may also include up to 70 phr of processing oil.Processing oil may be included in the rubber composition as extendingoil typically used to extend elastomers. Processing oil may also beincluded in the rubber composition by addition of the oil directlyduring rubber compounding. The processing oil used may include bothextending oil present in the elastomers, and process oil added duringcompounding. Suitable process oils include various oils as are known inthe art, including aromatic, paraffinic, naphthenic, vegetable oils, andlow PCA oils, such as MES, TDAE, SRAE and heavy naphthenic oils.Suitable low PCA oils include those having a polycyclic aromatic contentof less than 3 percent by weight as determined by the IP346 method.Procedures for the IP346 method may be found in Standard Methods forAnalysis & Testing of Petroleum and Related Products and BritishStandard 2000 Parts, 2003, 62nd edition, published by the Institute ofPetroleum, United Kingdom.

The rubber composition may include from about 10 to about 150 phr ofsilica. In another embodiment, from 20 to 80 phr of silica may be used.

The commonly employed siliceous pigments which may be used in the rubbercompound include conventional pyrogenic and precipitated siliceouspigments (silica). In one embodiment, precipitated silica is used. Theconventional siliceous pigments employed in this invention areprecipitated silicas such as, for example, those obtained by theacidification of a soluble silicate, e.g., sodium silicate.

Such conventional silicas might be characterized, for example, by havinga BET surface area, as measured using nitrogen gas. In one embodiment,the BET surface area may be in the range of about 40 to about 600 squaremeters per gram. In another embodiment, the BET surface area may be in arange of about 80 to about 300 square meters per gram. The BET method ofmeasuring surface area is described in the Journal of the AmericanChemical Society, Volume 60, Page 304 (1930).

The conventional silica may also be characterized by having adibutylphthalate (DBP) absorption value in a range of about 100 to about400, alternatively about 150 to about 300.

The conventional silica might be expected to have an average ultimateparticle size, for example, in the range of 0.01 to 0.05 micron asdetermined by the electron microscope, although the silica particles maybe even smaller, or possibly larger, in size.

Various commercially available silicas may be used, such as, only forexample herein, and without limitation, silicas commercially availablefrom PPG Industries under the Hi-Sil trademark with designations 210,243, etc; silicas available from Rhodia, with, for example, designationsof Z1165MP and Z165GR and silicas available from Degussa AG with, forexample, designations VN2 and VN3, etc.

Commonly employed carbon blacks can be used as a conventional filler inan amount ranging from 10 to 150 phr. In another embodiment, from 20 to80 phr of carbon black may be used. Representative examples of suchcarbon blacks include N110, N121, N134, N220, N231, N234, N242, N293,N299, N315, N326, N330, N332, N339, N343, N347, N351, N358, N375, N539,N550, N582, N630, N642, N650, N683, N754, N762, N765, N774, N787, N907,N908, N990 and N991. These carbon blacks have iodine absorptions rangingfrom 9 to 145 g/kg and DBP number ranging from 34 to 150 cm³/100 g.

Other fillers may be used in the rubber composition including, but notlimited to, particulate fillers including ultra high molecular weightpolyethylene (UHMWPE), crosslinked particulate polymer gels includingbut not limited to those disclosed in U.S. Pat. Nos. 6,242,534;6,207,757; 6,133,364; 6,372,857; 5,395,891; or 6,127,488, andplasticized starch composite filler including but not limited to thatdisclosed in U.S. Pat. No. 5,672,639. Such other fillers may be used inan amount ranging from 1 to 30 phr.

In one embodiment the rubber composition may contain a conventionalsulfur containing organosilicon compound. Examples of suitable sulfurcontaining organosilicon compounds are of the formula:Z-Alk-S_(n)-Alk-Z  IIIin which Z is selected from the group consisting of

where R¹ is an alkyl group of 1 to 4 carbon atoms, cyclohexyl or phenyl;R² is alkoxy of 1 to 8 carbon atoms, or cycloalkoxy of 5 to 8 carbonatoms; Alk is a divalent hydrocarbon of 1 to 18 carbon atoms and n is aninteger of 2 to 8.

In one embodiment, the sulfur containing organosilicon compounds are the3,3′-bis(trimethoxy or triethoxy silylpropyl)polysulfides. In oneembodiment, the sulfur containing organosilicon compounds are3,3′-bis(triethoxysilylpropyl)disulfide and/or3,3′-bis(triethoxysilylpropyl)tetrasulfide. Therefore, as to formulaIII, Z may be

where R² is an alkoxy of 2 to 4 carbon atoms, alternatively 2 carbonatoms; alk is a divalent hydrocarbon of 2 to 4 carbon atoms,alternatively with 3 carbon atoms; and n is an integer of from 2 to 5,alternatively 2 or 4.

In another embodiment, suitable sulfur containing organosiliconcompounds include compounds disclosed in U.S. Pat. No. 6,608,125. In oneembodiment, the sulfur containing organosilicon compounds includes3-(octanoylthio)-1-propyltriethoxysilane,CH₃(CH₂)₆C(═O)—S—CH₂CH₂CH₂Si(OCH₂CH₃)₃, which is available commerciallyas NXT™ from Momentive Performance Materials.

In another embodiment, suitable sulfur containing organosiliconcompounds include those disclosed in U.S. Patent Publication No.2003/0130535. In one embodiment, the sulfur containing organosiliconcompound is Si-363 from Degussa.

The amount of the sulfur containing organosilicon compound in a rubbercomposition will vary depending on the level of other additives that areused. Generally speaking, the amount of the compound will range from 0.5to 20 phr. In one embodiment, the amount will range from 1 to 10 phr.

It is readily understood by those having skill in the art that therubber composition would be compounded by methods generally known in therubber compounding art, such as mixing the various sulfur-vulcanizableconstituent rubbers with various commonly used additive materials suchas, for example, sulfur donors, curing aids, such as activators andretarders and processing additives, such as oils, resins includingtackifying resins and plasticizers, fillers, pigments, fatty acid, zincoxide, waxes, antioxidants and antiozonants and peptizing agents. Asknown to those skilled in the art, depending on the intended use of thesulfur vulcanizable and sulfur-vulcanized material (rubbers), theadditives mentioned above are selected and commonly used in conventionalamounts. Representative examples of sulfur donors include elementalsulfur (free sulfur), an amine disulfide, polymeric polysulfide andsulfur olefin adducts. In one embodiment, the sulfur-vulcanizing agentis elemental sulfur. The sulfur-vulcanizing agent may be used in anamount ranging from 0.5 to 8 phr, alternatively with a range of from 1.5to 6 phr. Typical amounts of tackifier resins, if used, comprise about0.5 to about 10 phr, usually about 1 to about 5 phr. Typical amounts ofprocessing aids comprise about 1 to about 50 phr. Typical amounts ofantioxidants comprise about 1 to about 5 phr. Representativeantioxidants may be, for example, diphenyl-p-phenylenediamine andothers, such as, for example, those disclosed in The Vanderbilt RubberHandbook (1978), Pages 344 through 346. Typical amounts of antiozonantscomprise about 1 to 5 phr. Typical amounts of fatty acids, if used,which can include stearic acid comprise about 0.5 to about 3 phr.Typical amounts of zinc oxide comprise about 2 to about 5 phr. Typicalamounts of waxes comprise about 1 to about 5 phr. Often microcrystallinewaxes are used. Typical amounts of peptizers comprise about 0.1 to about1 phr. Typical peptizers may be, for example, pentachlorothiophenol anddibenzamidodiphenyl disulfide.

Accelerators are used to control the time and/or temperature requiredfor vulcanization and to improve the properties of the vulcanizate. Inone embodiment, a single accelerator system may be used, i.e., primaryaccelerator. The primary accelerator(s) may be used in total amountsranging from about 0.5 to about 4, alternatively about 0.8 to about 1.5,phr. In another embodiment, combinations of a primary and a secondaryaccelerator might be used with the secondary accelerator being used insmaller amounts, such as from about 0.05 to about 3 phr, in order toactivate and to improve the properties of the vulcanizate. Combinationsof these accelerators might be expected to produce a synergistic effecton the final properties and are somewhat better than those produced byuse of either accelerator alone. In addition, delayed actionaccelerators may be used which are not affected by normal processingtemperatures but produce a satisfactory cure at ordinary vulcanizationtemperatures. Vulcanization retarders might also be used. Suitable typesof accelerators that may be used in the present invention are amines,disulfides, guanidines, thioureas, thiazoles, thiurams, sulfenamides,dithiocarbamates and xanthates. In one embodiment, the primaryaccelerator is a sulfenamide. If a second accelerator is used, thesecondary accelerator may be a guanidine, dithiocarbamate or thiuramcompound.

The mixing of the rubber composition can be accomplished by methodsknown to those having skill in the rubber mixing art. For example, theingredients are typically mixed in at least two stages, namely, at leastone non-productive stage followed by a productive mix stage. The finalcuratives including sulfur-vulcanizing agents are typically mixed in thefinal stage which is conventionally called the “productive” mix stage inwhich the mixing typically occurs at a temperature, or ultimatetemperature, lower than the mix temperature(s) than the precedingnon-productive mix stage(s). The terms “non-productive” and “productive”mix stages are well known to those having skill in the rubber mixingart. The rubber composition may be subjected to a thermomechanicalmixing step. The thermomechanical mixing step generally comprises amechanical working in a mixer or extruder for a period of time suitablein order to produce a rubber temperature between 140° C. and 190° C. Theappropriate duration of the thermomechanical working varies as afunction of the operating conditions, and the volume and nature of thecomponents. For example, the thermomechanical working may be from 1 to20 minutes.

The rubber composition is milled, calendared or extruded to form theapex, flipper, or chipper. The formed component will have the shortfibers with an orientation in the direction of processing, that is, asubstantial portion of the fibers will generally be oriented in adirection which is consistent with and parallel to the material flowdirection in the processing equipment. The rubber composition will havea degree of anisotropy, that is, a modulus measured in a directionconsistent with the processing direction will be greater than thatmeasured in a direction perpendicular to the processing direction. Therubber composition is incorporated into an apex, flipper or chipper.

With reference now to FIG. 1, a tire according to the invention containsa carcass ply 10 with a turn-up portion 12 and a terminal end 14. Theapex 16 is in the immediate proximity of the carcass ply turn-up 14including the area above the bead 18 and is encased by the carcass ply10 and carcass ply turn-up 12 or sidewall compound 20. The apex alsoincludes the area 22 located between the lower sidewall 20 and theaxially outer side of the carcass ply turn-up 12. The interface betweenthe bead 18 and the carcass ply 10 is a flipper 24. Located outside ofthe carcass ply 10 and extending in an essentially parallel relationshipto the carcass ply 10 is the chipper 26. Located around the outside ofthe bead 18 is the chafer 28 to protect the carcass ply 12 from the rim(not shown), distribute flexing above the rim, and seal the tire. Atleast one of apex 16, flipper 24, or chipper 26 comprises the rubbercomposition as described herein.

In one embodiment, the component is a flipper. In prior artapplications, a flipper typically comprises textile cord. In such aflipper application, the cord cannot be oriented in a zero degree radialdirection to the radial direction of the tire, due to the increase inradius experienced at the bead during tire build. Typically then, thecords are placed at a 45 degree angle with respect to the radialdirection of the tire, to allow for the radius increase and deformationof the flipper during tire build; see for example, U.S. Pat. No.6,659,148. By contrast, a with the short fiber composition of thepresent invention, the flipper may be constructed such that the shortfibers may be oriented at zero degrees with respect to the radialdirection of the tire. This is desirable to provide additional supportat the bead to counteract the directional stresses experienced at thebead. Thus, the flipper of the present invention is not restricted froma zero degree orientation, but may in one embodiment exist with theshort fibers substantially oriented in an angle ranging from 0 to 90degrees with respect to the radial direction of the tire. Bysubstantially oriented, it is meant that the flipper compound isdisposed such that with regard to the dimension of the flippercorresponding to that parallel to the direction of propagation throughthe flipper's fabrication process (i.e. calendar or extruded), thatdimension may be oriented at an angle ranging from 0 to 90 degrees withrespect to the radial direction of the tire. In another embodiment, theflipper may be disposed with the fibers oriented at an angle rangingfrom 0 to 45 degrees with respect to the radial direction of the tire.In another embodiment, the flipper may be disposed with the fibersoriented at an angle ranging from 0 to 20 degrees with respect to theradial direction of the tire. In another embodiment, the flipper may bedisposed with the fibers oriented at an angle ranging from 0 to 10degrees with respect to the radial direction of the tire.

The pneumatic tire of the present invention may be a race tire,passenger tire, aircraft tire, agricultural, earthmover, off-the-road,truck tire, and the like. In one embodiment, the tire is a passenger ortruck tire. The tire may also be a radial or bias.

Vulcanization of the pneumatic tire of the present invention isgenerally carried out at conventional temperatures ranging from about100° C. to 200° C. In one embodiment, the vulcanization is conducted attemperatures ranging from about 110° C. to 180° C. Any of the usualvulcanization processes may be used such as heating in a press or mold,heating with superheated steam or hot air. Such tires can be built,shaped, molded and cured by various methods which are known and will bereadily apparent to those having skill in such art.

The invention is further illustrated by the following nonlimitingexample.

EXAMPLE 1

In this example, the effect of adding a polybenzobixoxazole short fiberand an epoxidized palm oil to a flipper rubber composition according tothe present invention is illustrated. Rubber compositions containingdiene based elastomer, fillers, process aids, antidegradants, andcuratives were prepared following recipes as shown in Table 1, with allamounts given in parts by weight per 100 parts by weight of baseelastomer (phr). Sample 1 contained no short fiber and served as acontrol. Sample 2 and 3 included short fiber but no epoxidized palm oiland are comparative. Samples 4 included short fiber and epoxidized palmoil and is representative of the present invention. Cured samples weretested for physical properties, given in Table 2.

TABLE 1 Sample No. 1 2 3 4 Natural Rubber 100 100 100 100 Carbon Black46 36 30 36 Silica 0 0 8 0 PBO fibers¹ 0 8.6 8.6 8.6 Resorcinol 1.8 1.81.8 1.8 Process Oil² 6.5 6.5 6.5 0 Epoxidized Palm Oil³ 0 0 0 6.5Stearic Acid 3 3 3 3 Antidegradants⁴ 0.85 0.85 0.85 0.85 HMTA⁵ 1.3 1.31.3 1.3 Oiled sulfur 0.9 0.9 0.9 0.9 Zinc Oxide 7.5 7.5 7.5 7.5 Sulfur⁴1.4 1.4 1.4 1.4 Accelerator⁶ 1.1 1.1 1.1 1.1 Retarder⁷ 0.2 0.2 0.2 0.2¹Polybenzobisoxazole fibers, Zylon from Toyobo, 3 mm length, 12 microndiameter ²Low polycyclic aromatic oil of low viscosity ³Ultraflex EPO28, 33 from Performance Additives ⁴p-phenylene diamine and quinolinetypes ⁵Hexamethylenetetramine ⁶sulfenamide type ⁷phthalimide type

TABLE 2 Sample No. 1 2 3 4 Tear Strength Cure: 18 Min @ 150° C.; Test: @100 c, Pulling Speed = 50 cm/min, Adhesion To = Itself Tear Strength,N/mm 13.3 5.8 6.7 6.6 Cold Tensile D53504 Cure: 18 Min @ 150° C.; Test:Parallel to fiber direction; Test: @ 23° C., Pulling Speed = 20 cm/minElongation At Break, % 479.7 359.9 383.2 394.0 100% Modulus, Mpa 3.4 7.57.5 6.9 200% Modulus, Mpa 8.8 9.4 8.6 8.4 300% Modulus, Mpa 15.9 16.015.7 14.5 Tensile Strength, Mpa 29.6 20.4 21.7 20.9 Cold Tensile D53504Cure: 18 Min @ 150° C.; Test; Perpendicular to fiber direction; Test: @23° C., Pulling Speed = 20 cm/min Elongation At Break, % 480.6 334.1351.7 351.8 100% Modulus, Mpa 3.1 3.9 3.9 3.1 200% Modulus, Mpa 7.9 7.17.0 6.3 300% Modulus, Mpa 14.9 12.7 12.5 11.6 Tensile Strength, Mpa 28.914.8 15.7 14.7 Ring Modulus Cure: 18 Min @ 150° C.; Test: @ 23° C.,Pulling Speed = 50 cm/min Elongation At Break, % 471.1 310.9 351.5 362.6100% Modulus, Mpa 3.1 6.1 5.9 5.2 200% Modulus, Mpa 8.2 9.1 8.9 8.0 300%Modulus, Mpa 15.0 14.8 14.2 13.1 Tensile Strength, Mpa 23.2 — 14.9 14.5MDR 2000 Light Tire Test: @ 150° C. Minimum torque, dN · m 2.4 2.2 2.01.8 Maximum torque, dN · m 22.9 25.0 23.0 21.4 Delta Torque, dN · m 20.622.8 20.9 19.6 Time To Minimum S′ (Mean), Min 0.3 0.4 0.4 0.4 Time ToMaximum S′ (Mean), 18.0 19.5 22.7 16.5 Min T90, Min 8.6 10.5 12.6 9.4Reversion 1, Min 46.4 29.3 32.5 24.1 RPA 2000 Cured @ 150° C. Test: @100 c, Frequency = 11 Hz, Strain Sweep Tan delta, 1% strain 0.071 0.0550.046 0.046 Tan delta, 5% strain 0.113 0.087 0.075 0.076 Tan delta, 10%strain 0.113 0.085 0.075 0.079

Rubber samples were milled into a sheet and cut into tensile testspecimens. Tensile test specimens were cut in two orientations, one withthe test pulling direction parallel with the milling direction of thespecimen, and one with the test pulling direction perpendicular with themilling direction of the specimen. In this way, the effect of fiberorientation (generally in the direction of milling) and thus theanisotropy of the rubber composition was measured. The tensile sampleswere then measured for stress at various strains. A stress ratio,defined as the (stress measured in the direction parallel to the millingdirection)/(stress measured in the direction perpendicular to themilling direction) was then calculated for each strain. The results ofstress measured in the direction parallel to the milling directionversus strain are shown in FIG. 2. The results of the stress ratioversus strain are shown in FIG. 3.

As seen in FIG. 3, the stress ratio for Samples 2 and 3 containing theshort fibers shows a maximum at about 10 to 15 percent strain,indicating a strong anisotropic reinforcing effect of the fibers in thesample. Such anisotropy is important for applications such as apexes,flippers, and chippers where anisotropic reinforcement is advantageousdue to the directional stresses experienced by these tire components atlow strains. By comparison, control sample 1 with no fiber shows no suchanisotropy. However, a maximum stress at low strain as seen for Samples2 and 3 indicates interfacial failure between the fiber and rubbermatrix at a lower strain than is desirable. Sample 4, containing shortfibers and epoxidized palm oil, shows a maximum in stress at about 25 to30 percent strain, much higher than for Samples 2 and 3. The strain atwhich the peak stress occurs for Sample 4 indicates a better interactionbetween the fibers and rubber matrix, due to the presence of theepoxidized palm oil.

As seen in FIG. 3, the stress ratio for Samples 2 and 3 containing theshort fibers shows a maximum at low strain, indicating a stronganisotropic reinforcing effect of the fibers in these samples. However,Sample 4 containing the short fibers and epoxidized palm oil shows apeak at higher strain with a much broader yield as compared with Samples2 and 3, wherein a sharp yield is observed at a lower strain. Suchbehavior indicates that the inventive Sample 4 demonstrates superioradhesion of the short fibers to the rubber matrix, as illustrated by thebroad yield peak at relatively higher strain. By contrast, the sharpyield at relatively lower strain for Samples 2 and 3 demonstrates muchpoorer adhesion by fibers in Sample 4. Such anisotropy as demonstratedby Sample 4 is important for applications such as apexes, flippers, andchippers where anisotropic reinforcement along with good fiber adhesionis advantageous due to the directional stresses experienced by thesetire components at low strains. The superior adhesion and broad yield atlow strain for the inventive Sample 4 as compared to Samples 2 and 3 issurprising and unexpected. Typically, short fibers show behaviordemonstrated by Samples 2 and 3, with a sharp yield at low strain,indicating poor adhesion and consequent inability to utilize anyanisotropy in the compound at strains typically seen in apex, flipperand chipper applications. By contrast, Sample 4 according to the presentinvention shows much superior adhesion and a broad yield at higherstrain, indicating that the compound sample will better perform in anapex, flipper or chipper application.

While certain representative embodiments and details have been shown forthe purpose of illustrating the invention, it will be apparent to thoseskilled in this art that various changes and modifications may be madetherein without departing from the spirit or scope of the invention.

1. A pneumatic tire comprising a flipper, the flipper comprising arubber composition, the rubber composition comprising a diene basedelastomer and from 1 to 8.6 parts by weight, per 100 parts by weight ofelastomer (phr), of a polybenzobisoxazole (PBO) short fiber having alength ranging from 0.5 to 20 mm and a thickness ranging from 10 to 30μm, and from 1 to 30 phr of an epoxidized palm oil.
 2. The pneumatictire of claim 1, wherein the epoxidized palm oil has 1 to 5 percent ofunsaturated bonds converted to epoxy groups.
 3. The pneumatic tire ofclaim 1, wherein the epoxidized palm oil has 2 to 4 percent ofunsaturated bonds converted to epoxy groups.
 4. The pneumatic tire ofclaim 1, wherein the epoxidized palm oil is present in a concentrationof 5 to 15 phr.
 5. The pneumatic tire of claim 1, wherein the flipper isdisposed with the short fibers substantially oriented in an angleranging from 0 to 90 degrees with respect to the radial direction of thetire.
 6. The pneumatic tire of claim 1, wherein the flipper is disposedwith the short fibers substantially oriented in an angle ranging from 0to 45 degrees with respect to the radial direction of the tire.
 7. Thepneumatic tire of claim 1, wherein the flipper is disposed with theshort fibers substantially oriented in an angle ranging from 0 to 20degrees with respect to the radial direction of the tire.
 8. Thepneumatic tire of claim 1, wherein the flipper is disposed with theshort fibers substantially oriented in an angle ranging from 0 to 10degrees with respect to the radial direction of the tire.